Hydraulic brake



April 4, 1939. T. P. CHASE HYDRAULIC BRAKE Filed Nov. 1, 1957 Snnentor ZkiozzVPC/msa connection with the hydraulic brake sysj tems asused on vehicles it has been proposed to provide servo devices to supplement the manu- V ally appliedfiorce acting to depress theplunger' within 'thejmaster cylinder. This invention is concernejdfwith such supplementary mechanism. An object of the'invention is to associate .with the master cylinder a'cylinder and piston assembly wherein the piston moves in response to di1-' "to take upbrake shoe clearanceland, if desired, H to spreadthe shoes with light pressureiagainst ferentiall air pressures and with afforce suiiicient ,I the drums.

i As a further object the invention aims to con-f trol theiair pressure device by. valve means which shall be (responsive to movements of the accelerator pedal.

i for the purpose of reducing the brake pedal pres- 'tion is toybe eflective for all degrees ofbraking.

pedal.

sure to a predetermin'ed eiitent and such reduc the" action occurring in response to aflrelease of the manual pressure applied to the accelerator Other objects. and advantages'including efficient operation and simple construction "will be understood from the following description. In the drawing:

Figure l'is a transverse sectionthrough the I master cylinder and the associated servo device. Figure 2; isfan enlarged section of a portion of 5 the masterfcylinder and reservoir.

Figure 3 'is a section on line 3-3 of Figure 1.

t Figure 1 is aview in elevation, partly in section, as seen from line 4-4 of Figure 3.

It will be understood that the invention has been primarily designed for use with the master cylinders of hydraulic brake systemsas used on vehicles. It is unnecessary to illustrate the whole vehicle, the toe board being shown on the drawing and designated by numeral '1. board the accelerator pedal. I i is' pivoted at 9. The invention is not concerned with the parts by which the pedal ll controls the throttle of the engine but there is shown a lever I3 pivoted to the toe board at l5. A link. :1 connects this lever Hi to the throttle valve, not shown, and the lever is depressed by a plunger l9 pivoted thereto and reciprocated by the pedal H.

A bracket 21 secured to the toe board supports, the upper end of two cylinders 23 and 25. Cylinder 23 together with its axial extension 21 forms the master cylinder of the hydraulic brake system. The upper end of the master cylinder has a cylindrical guide 28 for the passage of a finer-1t rHIiDRAULI CBRA KE H i TheronP. chase, Detroit, Mich, w

" a eral Motors Corporation, Detroit, Mich a cor- -P ratim -D leW t. e Applicationflofvember 1, 1937, Serial No. 172,099

To the toe FPATE N OFFICE scam. (01. 192-4) h plunger 3|. Suitable sealing means 33 and a flexible boot 35 are shown, the functions of these elements being obvious. A lower plunger guide is shown near the end of cylinder 23 and identifled by numeral 31. The extreme end of cylinder 23 is formed with a shoulder to receive a flange 39 of guide 31, there being an annular recess 4| at the end of guide 3|.and radial passages 43 extending therefrom. Passages 43 communi- -cate with an annular groove 45 formed in cylcommunication with the reservoir by means of s s i h s s H channel 5| formed in guide 31. As aj further object the structure designed A rubber seal 53 equipped with an angular the wall of the cylinder 21. The end of the plunger has an axial passage 55' communicating with radial passages 51 so that in the fully retracted position of the plunger the region within the cylinder 2'! may communicate with the reservoir by means of the passagesabove described. At the end of the master cylinder is apertured plug 55 for connection with the pipe line represented by numeral 6| extending" to the several wheel cylinders as usual. A pressure valve may be mounted at the outlet of cylinder 2? if it be desired to maintain a limited degree of pressure in the wheel cylinders and pipe lines. The valve 63 is illustrative of such an expedient. Between this valve 63 and the seal 53 is a spring 65 which serves to hold the seal in position and to ofier resilient resistance to the flow of fluid back to the master cylinder through the'valve 63. A non-return valve represented as a whole by numeral 61 is shown as operatively related to the reservoir and cylinder 21. This valve is adapted to be closed when pressure is developed within cylinder 21 but to open under suction to admit fiuldto said cylinder 2'! from the reservoir.

Cylinder 25 in addition to its. support by bracket 2| is made rigid with cylinder 21 by a bracket 69, this bracket serving also as an end closure for cylinder 25. Cylinder 25 has an n per end closure II for the passage of the piston rod 13 which is attached to a piston I5, the latt-er being as shown in the drawing. A spring 11 in abutment with end closure 69 engages the piston 15 and is adapted to be compressed by an inward reciprocation of said piston. A valve 18 is attached to the end closure i I by fastening screws II. The valve has an opening I: registering with an opening II in the end closure and leading to a longitudinal passage 81 in the main portion of the valve. Reciprocable within passage I1 is a valve plunger 8!. The plunger is formed with a recess ll between its major portion and an end disc II. The wall of passage 81 is provided with a stop ll. Airopenings in the wall marked 85 are so located that they are covered by the end disc to when the plunger approaches and engages the stop 93. Other apertures 91 open into a recess I! within an end-cap Ill, the latter having a pipe connection I for communication with the. engine intake-manifold. The phmger II is connected by a link III to the lever IS.

A pedal pad III is suitably mounted on the end of plungerll. This pad is also connected to the piston rod 13 whereby the hydraulic master cylinder maybe'actuated by manual pressure on the pedal pad or by differential air pressure on the opposite sides of piston II.

The operation of the brakes by the pedal pad and the master cylinder is conventional. Depression of the pedal reciprocates the plunger through seal". This decreases the capacityof cylinder 21 and the developed pressure insures I mit fluid to cylinder 21 in the event that this device in the following way.

the closure of valve 81. The movement of the plunger also cuts on communication with the reservoir through passages 51 and The transmission of a fluid medium throu h pipe lines it applies the brakes. Such depression of I the brake pedal also depresses piston 15 against spring 11. The parallel relation of piston rod 13 with plungerv 3i prevents any rotation of plunger it about its longitudinal axis. when the brake pedalis returned by spring 11 or by any other return spring the valve 61 may open to adreturn movement develops suction. when the plunger is fully retracted the reservoir com- ,municates with cylinder 21 by way of es 5, ll and 51. a

The above operation is modified by the servo the brake the'accelerator pedal is completely released, its release operates through the instrumentality of lever l3, link I" and plunger 89 to open the cylinder 25 to the engine vacuum by way'of passages 85, 83, 81 and 99, the communication being made possible by the position of the recess 9! in the plunger. Figures 3 and 4 show the parts in this position of retracted accelerator.

- The normal air pressure above piston 15 thereupon moves the piston 15 downwardly and its rod pulls upon the pedal and reciprocates the plunger 3| within the master cylinder. It does this even if no pressure is applied manually to the brake pedal. The size of cylinder 25 is so selected that a predetermined force is applied, a force sufllcient' to move the shoes into contact with the drum and, if desired, to exert a slight pressure. If, then, manual pressure is applied to effectively spread the shoes against the drum, the

If before applying manual pressure required is reduced below that which would be requiredin the absence of the servo and owing to the length of the air cylinder the reduction in the required manually applied' the suction opening and to open the cylinder 2! to atmospheric air by uncovering the openings I. The low rate spring 11 thereupon restores the brake parts to completely released'position.

I claim:

1. Hydraulic brake applyingmeans comprising a master cylinder, 9. plunger reciprocable therein, a pedal pad carried by said plunger, an air cylinder, a piston therein having a rod projecting from the cylinder, said rod being parallel to said plunger and connected to said pad whereby the plunger is restrained from rotation about its longitudinal axis, a conduit opening to said air cylinder and adapted to be connected to a source of suction, a valve in said conduit, an accelerator pedal, connections therefrom adapted .to'open said valve to the atmosphere when the accelerator pedal is depressed andto said source of suction when released.

2. The invention defined by claim 1, together with 'a low rate spring in said 'air cylinder adapted to return the plunger to brake released position when the accelerator pedal is depressed.

3. The invention defined by claim L sa'id air cylinder being elongated and of such diameter as to apply a forceto said plunger onlyfsuiilcient to take up brake shoe clearance and to ,lightly apply the brakes, whereby a relativeiy low manually applied force is required throughout the brake applying'movement of the plunger;

4. Hydraulic brake appiyng means comprising a direct acting master cylinder, a parallel rela-' tively small but elongated air cylinder, a' directly applied plunger reciprocable'lnihe masterf cylinder, a piston witha rod in the air cylinder, a manually operable pad connected to the adjacent ends of'the plunger and piston was 1:

duit for connecting said air cylinder to a'sou'rce of-suction, a valve in said conduit, a throttle controlling accelerator, means associated with said accelerator to control said valve, the "combined manual and suction iorcesacting on 'saidplunger in response tothe opening of said valve to permit theprovision of a relatively highmech'anical advantage in the brake operating system, the structural arrangement of the plunger," piston rod and pad preventing rotation of'the plunger about its axis. H

5. The invention defined by claim 4 together with a low-rate return spring within saidair cylinder and acting on the piston thereof.

"rH Ro'n P. c asm. 

